7. ENTITY RELATIONSHIP MODELLING
Up to this point we have made several references to the concept of relationship. Now, we will make our understanding of this concept more complete. A relationship is an association amongst entities. Relationships will have justification in business rules, in the way an enterprise manages its business.
There are several ways of classifying relationships, according to degree, participation, cardinality, whether recursion is involved, and whether a relationship is identifying or not.